The bowfin, Amia calva is a facultative air breathing fish which uses its respiratory swimbladder to augment oxygen uptake in normoxia at 30 degrees C. It does not die however, when denied access to the surface at this temperature. The bladder RQ is 0.21 while the gill RQ is 1.61 and thus most of the CO2 is excreted into the water across the gills. In aquatic hypoxia some of the oxygen taken up via the swimbladder is lost to the water across the gills. However CO2 excretion across the gills is maintained at the same rate as that found in normoxia.